1. Field of the Invention
The present invention pertains to valves having rotary valve elements mounted on shaft members or trunnions which are journaled in the valve body and, more particularly, to an assembly for securing the valve element to the shaft member.
While the invention is particularly suited to disk-type or butterfly valves, it may also be used with other types of rotary valves such as ball valves, plug valves, etc. In typical valve assemblies, the valve element is mounted in the valve body using a shaft which is rotatably journaled in the valve body. One end of the shaft member extends outwardly of the valve body to provide a valve stem portion which can be operated by a handle or valve actuator. It is necessary to fix the valve element with respect to the shaft so that they will rotate as a unit when the stem is turned.
The performance of such rotatable valves is, to a great extent, determined by the quality and integrity of the connections between the shaft member and the valve element. These connections should be capable of transmitting torque loads of high magnitude in either direction with minimum rotative and axial play between the shaft member and valve element. Ideally, the connection should provide for such torque transmission while minimizing the consequent reduction in torque carrying capacity of the shaft member. It is also desirable that the connections be designed so that the shaft member, valve element and associated parts can be easily and inexpensively manufactured with conventional equipment so that the apparatus can be easily assembled and disassembled.
2. Description of the Prior Art
In conventional trunnion mounted valve elements, trunnions or shaft members are usually fixed to the valve element either by pins or some type of key. In the pin-type of connection, the pin extends through bores in the shaft and valve element respectively. It is not necessary only that these bores be perfectly aligned but also that there be an extremely tight fit between the pin and the bores to avoid play. Thus, close tolerances and/or machining of the parts during assembly are required resulting in high costs and inconvenience in the use of the pin-type connection.
In the key-type of connection, on the other hand, the shaft member must be machined to receive the key. This may involve altering the circular cross-sectional configuration of one section of the shaft to make it square, hexagonal, DD or the like. Alternatively, a slot may be cut in the shaft member to receive the key. In either case, a substantial amount of metal is removed from the shaft member in the machined section diminishing its cross-sectional area. This in turn drastically reduces the torsional strength or torque carrying capacity of the shaft member. For example, by machining the shaft section from circular to a square cross-sectional configuration, its torsional strength is reduced by over sixty percent. Moreover, key connections, like pin connections, require close tolerances for satisfactory performance which in turn necessitates complex manufacturing processes resulting in high costs. Moreover, conventional key connections only prevent relative rotation between the shaft members and valve elements and do not provide axial restraint. Accordingly, additional means must be provided for fixing the shaft members axially with respect to the valve element thus further raising the cost of manufacture.
Another disadvantage of both pinned and keyed connections is that even when the necessary tight fits are provided, wear of the parts during use of the valve eventually begins to allow the undesirable play which the tight fits prevented.
In Australian Pat. No. 515,047, incorporated herein by reference, there is disclosed an assembly for securing a rotary element such as a valve element to a shaft which utilizes a torque transmission member compressively urged against a flat on the shaft member. The torque transmission member is threadedly received in a bore which intersects a bore in the valve element through which the shaft extends. The torque transmission member has a substantially flat, circular end surface which lies parallel to and abuts the flat. The diameter of the end face of the torque transmission member is greater than the distance between the side edges of the flat but less than or substantially equal to the distances between the end edges so that the end face extends laterally beyond the side edges of the flat but lies between the end edges.